This invention pertains generally to signal processing, and specifically to the analysis of radar and communications signals. More particularly, it is directed to a channelized hybrid acousto-optic signal processor for real time analysis of signals having a high frequency carrier modulated by an envelope signal.
Fine frequency resolution spectral analysis of wide bandwidth signals is a challenging task found in many areas of signal processing. The task becomes even more challenging if the information must be processed in real-time. To perform this task, several acousto-optic architectures utilizing optical technology have been developed in the past. One-dimensional acousto-optic space-integrating architectures can analyze wide bandwidth signals, but the frequency resolution is limited. One-dimensional acousto-optic time-integrating architectures offer increased frequency resolution capability, but smaller bandwidths must be analyzed to obtain this resolution. The prior art discloses a number of combinations of space- and time-integrating processors developed to obtain large time-bandwidth product spectral analysis. The combinations include two-dimensional space-integrating, two-dimensional time-integrating, and two-dimensional hybrid space- and time-integrating processors.
In some applications, the signals of the interest consist of a high frequency carrier modulated by an envelope signal. It is convenient to classify these signals by both the carrier frequency and the spectral characteristics of the envelope signal. For the purpose of this application, the envelope signal will be defined specifically as the instantaneous power in the signal that modulates the high frequency carrier. The frequency resolution for analysis of the carrier frequency can be coarse, but finer resolution is required for the envelope spectrum. The present invention is directed to a novel optical processor that uses two acousto-optic cells in a crossed-cell configuration, developed to perform this type of analysis. Space-integration is used to channelize signals according to carrier frequency and time-integration is used to obtain the spectrum of each envelope signal used to modulate a particular carrier frequency.